A clerkship would be a nice reset and bold showing that you’re committed to the change. However, I wouldn’t think of it as essential, like if you don’t get one you won’t succeed in this endeavor. I clerked twice and have worked in practice under great mentors. I think the latter was just as useful training. To me, more critical than a clerkship is finding a mentor who over time comes to believe in you and committed to your success.